Chemical Inventions and the Doctrine of Equivalents

In U.S. patent law, the Doctrine of Equivalents allows a patent owner to claim infringement by a product or process that is outside the scope of the patent claims but close enough to be considered an equivalent. To qualify as an equivalent, however, the product or process that is accused of infringement is closely scrutinized, and two alternative tests have evolved in the patent courts. This column discusses those alternative tests and highlights the difficulty in meeting the test requirements with chemical inventions.